If you’re running BeOS Pro, you’ve already got a full suite of development tools (including an integrated IDE, the gcc compiler, linker, debugger, and tons of interesting sample code).
If you’re running Personal Edition, these items are not present by default, to save on download size. However, these tools are still available for free, at ftp://ftp.be.com/pub/beos/.
Note that the downloadable development tools package does not include the tons of sample code available in Pro Edition. To get your hands on this, you’ll need to grab archives individually from ftp://ftp.be.com/pub/samples/.
What’s not obvious once you download the DevTools package is where to put it. The package needs to be expanded into /boot in order for everything to work properly. Either move the zip to the root of your boot drive before double-clicking and expanding, or edit the path in Expand-o-Matic to read /boot.